This invention relates generally to circuit breakers and more particularly to arc fault detecting circuit interrupters.
An arc fault circuit interrupter protects against electrical discharge characterized by low and erratic current resulting, for example, from a damaged extension cord or an improperly installed wall receptacle. Arc fault interrupters are commonly configured in one-pole and two-pole circuits that utilize current transformers and current sensors to detect arc faults and over-currents. When such a hazard is detected, a trip device is activated to open the circuit.
Bimetal thermal trip devices typically include a bimetal current sensor in a two-pole circuit breaker. A ground fault detecting current transformer is associated with one of the two poles. If the breaker trips when no power is sensed on a side of the current transformer, and if the bimetal current sensor is at a potential equal to that of the pole conductor associated with the transformer, a large spurious signal may enter an over-current sensor circuit and cause the breaker to work incorrectly.
One-pole arc fault circuits have been adapted to two-pole breaker circuit configurations. Such circuits typically are complex, particularly where powered from a pole not associated with the transformer. Thus, for example, one known two-pole configuration references three separate ground potentials and includes two opto-couplers. A ground reference for each over-current sensor is referenced to the bimetal resistor at its associated pole potential, and power for each sensor circuit is derived from a neutral conductor. The trip circuit contains a ground leakage detection circuit and is powered by a full-wave power supply. Over-current trip signals are relayed to the trip circuit by the two opto-couplers. As the above described circuit illustrates, prevention of spurious trip signals has entailed additional power supply circuitry and use of opto-couplers or other devices capable of transferring a signal across high voltages.
In an exemplary embodiment, a circuit for detecting arc faults and over-currents includes a ground fault circuit and two over-current detection circuits. Each over-current detection circuit includes a Hall effect current sensor configured to determine a current in a corresponding pole conductor. The ground fault and over-current detection circuits are referenced to a single ground and configured to receive power from a single power supply. In operation, a current signal is sensed by a Hall effect sensor with reference to the single ground and without a metallic connection between the sensor and the pole conductor.
The above described circuit allows a two-pole breaker circuit to be configured in a form similar to a one-pole circuit and also eliminates tripping caused by spurious signals from bimetal sensors.